According to a known design, an electromagnetic contactor for a power circuit comprises a mobile contact which is fitted on a control rod. The mobile contact is designed to come into contact with power terminals which are arranged in a contact chamber. This contactor is used for example in order to control the activation of an electric motor of a starter of an internal combustion engine.
More specifically, an electromagnetic contactor 1 shown in FIGS. 1a to 1c is provided with a mobile core 3, a fixed core 4 and a metal housing 6, or vessel, in which there are arranged a pull-in coil 81 and a hold-in coil 82 which are fitted on an insulating annular support 9. This support 9 and the front end of the housing 6 are provided centrally with a passage for the mobile core 3.
An end of the mobile core 3 is connected to a pivoting lever (not represented), which acts for example on the launcher of the starter, as described in document FR2795884. This therefore shows the tooth-against-tooth spring 10 which can be compressed in the case of lack of direct penetration of the pinion of the launcher (not represented) into the starter ring which is connected to the thermal engine and the connection rod 12 which is connected to the pivoting lever.
The other end of the mobile core 3 is designed to act on a front end of a control rod 15 by thrusting through a central hole 16 in the fixed core 4, in which the front part of the rod 15 is fitted such as to slide.
The control rod 15 supports a contact plate 21. The contact plate 21 extends transversely relative to the rod 15, in order to cooperate with two electric terminals 26a, 26b of an electric power circuit, and to establish an electrical contact between them. One of the terminals 26a is designed to be connected to a positive terminal of the battery, the other terminal 26b being designed to be connected by means of a cable to brushes of the electric motor with positive polarity.
The two terminals 26a, 26b are secured and supported by a cap 30 made of electrically insulating material which ensures the closure of the rear of the vessel 6. The cap 30 is secured by folding of material of the free end of the vessel 6 back onto the cap 30.
The rod 15 supports an axial compression spring 32 which is arranged between a shoulder 33 of the rod 15 and a face of the mobile contact 21. The contactor 1 also comprises a return spring 38 which is arranged between the cap 30 and a stop of the control rod 15.
In addition, a micro-solenoid 41 is integrated in one of the terminals 26a. This micro-solenoid 41 comprises a coil 42 which is secured relative to the 30, and a core 43 which is mobile in translation relative to the cap 30. This core 43 is mobile between an initial position, in which an end of the core 43 projects relative to the terminal 26a, such as to prevent electrical contact between the plate 21 and the terminal 26a; and a final position in which the core 43 permits electrical contact between the plate 21 and the terminal 26a. A return spring 46 is supported firstly against the base of the cap 30, and secondly against an end head of the core 43 which is situated opposite the cap 30. This spring 46 ensures the return of the core 43 to the initial position further to a cut-off of the supply of the micro-solenoid 41. Reference can be made for example to documents FR2923869 or FR2959891 for further details of such a device.
The mobile core 3 is initially in the so-called position of rest, in which the core 3 is spaced from the fixed core 4. The plate 21 is then in a deactivated position in which the plate 21 is spaced from the contact terminals 26a, 26b. The micro-solenoid 41 is then not supplied with power, and its core 43 is maintained in the initial position by the return spring 46.
Further to a demand by the engine computer, the coils 81 and 82 are activated electrically, and then create a magnetic field. This magnetic field permits the axial displacement of the mobile core 3 in the direction of the fixed core 4. The rear end of the mobile core 3 comes into contact with the front end of the control rod 15, then displaces the rod 15 axially through the hole 16, in the direction of the rear of the contactor 1, until the said mobile core 3 is supported against the fixed core 4 in a so-called magnetised position.
The displacement of the rod 15 has the effect of displacing the plate 21 into a so-called pre-engagement position, in which the plate 21 is in contact with the terminal 26b, but is kept spaced from the other terminal 26a. For this purpose, power has previously been supplied to the micro-solenoid 41, such that its core 43 can withstand the force applied by the plate 21, and therefore be maintained in the initial position. The compression spring 32 is then compressed.
When a starting demand is issued by the engine computer, the supply to the micro-solenoid 41 is cut off, such that the core 43, which can no longer withstand the force applied by the plate 21, can then go into the final position represented in FIG. 1c. The contact plate 21 then establishes contact with the two terminals 26a, 26b, which makes it possible to supply the electric motor of the starter with power.
The problem consists in the fact that the compression spring 32 has stored mechanical energy such that when the current which passes through the coil 42 of the micro-solenoid 41 is cut off, in order to make the contact plate 21 go from the pre-engagement position to the active position, the core 43 will tend to oscillate between its final position and its initial position, which will generate impacts with the plate 21, and thus a risk of reopening of the electrical contact between the plate 21 and the terminals of the contactor 26a, 26b. 